Selective antenna circuit



, 7, 1933. G. w. GILMAN 1,934,602

SELECTIVE ANTENNA CIRCUIT Filed Oct. 6, 1932 2 Sheets-Sheet l Fix/7.6

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G. WGIZIM/an ATTORNEY Patented Nov. 7, 1 933 PATENT} OFFICE SELECTIVE ANTENNA CIRCUIT George W. Gilman, Lawrenceville, N. J., assignor to American Telephoneand Telegraph Company, a corporation M New York Applicationoctober 6-, 1932. Sferial No. 636,591

24' Claims. (01. 250-43) This'invention relates to selective antenna circuits and is a further development of the inventions disclosed in my applications, Serial No. 480,246, filed September 6, 1930 and Serial No.

,5 569,778, filed October'19, 1931. v n The purpose of the invention is to devise an antenna system operative on different frequencies and so connected that the frequency of the entire station may be changed simply by chang- 10 ing the frequency of the wave used.

Another purpose is to accomplish this without the use of mechanical or electrical switching means calling for any moving. parts.

More specifically the purpose of the invention isto devise circuit arrangements by which, and

in which, the antenna shall at all times be operative for any or all of a number of chosen operat- 7 ing frequencies either as a transmitting or a receiving antenna under such conditions that there will be impedance matching between, different portions of ,thecircuitfor each of the operating frequencies, there will be proper impedance terminationsto prevent undesirable reflections, .and there will be prevention of transfer of energy from the local circuit appropriate for oneoperat ing frequency to the local circuit appropriate for another.

The invention will be better understood by 7 reference to the following specification and acc ompanying drawings, .in which Figure 1 shows naling on two frequencies; Figs. 3a, 3b. and 3c illustrate specific means for the impedance matching; Fig. 4 illustrates the termination of an. antenna system in a manner to prevent unde- 40 sirable reflection; Fig.5 shows the application of this to an antenna system adapted foroperatingon a plurality of frequencies; Fig. 6 shows in.

greater detail the application to a system for two operating frequencies; Figs. '7 and 8 illustrate the application of my invention to a system comprising a plurality of terminal stations associated with a single antenna, with meansto prevent transfer of energy from one terminal station to another; Figs. 9 and 10 show combinations of .impedance matching and prevention of transfer .of power between local circuits; Figs. 1-1 and 12 show the application of. my invention to proper impedance termination and prevention of transfer of energy between local circuits; Fig. 13 shows a plurality of antennae and a plurality of point which is, at a distance from the junction of terminal stations joined by a single transmission line, but with means for preventing transfer of energies from the one to the other, and Fig. 14 shows in greater detail the application of all of these features in'one system.

The invention is based on various circuit arrangements of the selective circuits shown in' my applications, Serial Nos. 480,246 and569,7'78 mentioned above. In the latterapplication it was shown how two selective circuits couldbe obtained by properly bridging short sections of line, comprising two parallel wires, across a transmission line. Each of these sections of line or, selectors will operate to exclude an undesired wave from a circuit, and yet not interfere with the wave to be transmitted. One of these selectors or short transmission lines is openat one endand short=circuited at the other, and is of a length equal to an odd multiple of a quarter wave at thefre'quency to be passed. The other selector is open at both ends and is of a length equal to a multiple of a half wave at the frequency to be passed. a I V The "terminal impedance of both of these bridging selectors is very h gh, substantially'inso finite,if attenuation is assumed negligible, irrespective of the point of attachment, providing sa'fd pointof attachment is not at a distance from one of the open ends equal to an odd multiple of a quarter wave.- Under the latter condition, however, the terminal impedance is very low, substantially zero, if attenuation is assumed negligible. Utilizing this characteristic the selectors are attached to the transmission line at a point along the selector length which is at a distancefrom one of their open ends equal to an odd multiple of a quarter wave at the frequency to be,.excluded. Thus, these selectors shunt the'lin'e with a high impedance forthe frequency to be passed and with a low impedance for the frequency to be excluded.

' In a system comprising two circuits .inparallel a selector is bridged across each branch at a the branches equal to anodd'multiple'of a quarter wave atthe frequency to be excluded from that particular branch. shunting the line; with a low impedance at this particular point results in the crcuit offering a fveryhigh impedance'at the junction point to the undesired wave. It was also shown in the above mentioned application, that in the special case of a two branch circuit the selector on the branch over which the longer wave; is to be transm tted 'should preferably bea short-circuited quarter wave selector, while should preferably be an open line of half wave length.

Referring now more specificallyto Fig. 1, as a single line diagram, there is shown a. terminal or local station which may be a transmitter or receiver, operative at the frequencies f1, f2. f3 and connected with an antenna A. operative at the same frequencies. A transmission line would ordinarily extend from the terminal station to the antenna. In general, in such a station, the impedance of the terminal station and of the antenna are different, the terminal station as a rule having a small impedance compared to that of theantenna. Furthermore, these impedances are a function of the frequency. It is well known that in any transmission circuit reflection occurs at points of impedance irregularities, and these reflected waves are such as to seriously upset the best operation of the antenna system. For this reason I desire-to obtain impedance matching be-' tweenthe terminal station and the antenna, and to do this at each of the operatingfrequencies without the necessity of mechanical switching or the use of other moving parts. The impedance matching may be obtained by any suitable devices suchas impedances ZiQZz and Z3, and I bring these into operation so-far as Fig. 1 is concerned, by dividing the transmission line L into three parallel circuits, each containing one of the impedance matching devices, and then bringing acs e circuits together again to continue to the antenna A. It is important, however, that onlyf'power corresponding to the frequency of.

applications, SerialNos. 480,246 and 559,778. I

haveshown the'seselectors by, the reference letters S and S, usng in addition with each of these 7 letters a double subscript, the first subscript indicating the frequency to be passed, andthe second subscript the frequency to be excluded. Thus, S13 would indicate that f1 is to be passed andjs is to be excluded. In this case also, since there is a terminal stat-on on the one side of the im pedance matching devices and an antenna fon the other side, there are two junction points at which, exclusion is to. be exercised. 'It istheiefore necessary. to have'selectors on both sides of the matching devices, and Iuse the letter S to indicate the selector on the side towards the terminal station and S the selector on the side "towards the antenna. Also, in accordance with my previous invention, "each selec lengths of the wave to be excluded, all this being clearly shown in Fig. 1. Inthis figure it is to be understood that thetransm ssion line L is comparatively long, whereas the distances given over to the parallel paths and to the connection from the junction point CT to the antenna A, are both about as short as physically convenient. Under theseconditions, theonly one of the operating frequencies Whichwill pass through the branch 1 is the frequency ii, the only frequency through on the branch for the shorter Wave the selector the branch 2' is f2, and the only frequency through the branch 3 is f3.

' The impedance matching devices Z1, Z2 and Z3 may take on a number of forms and the specific form which they take on does not constitute a part of my invention. A suitable device would be a transformer of the type shown in Fig. 3a, and since, in general, the impedance of'thean tenna A will diifer from the surge or characteristic impedance of the transmission line, the transformer will have an impedance ratio other than unity.

The windings of such a transformer should preferably have bridged across them variable condensers in orderthat the circuits may be tuned to the desired frequency. Another form which the matching device may take on is that of Fig. 3b, which. consists of a tuned autotransformer with adjustable contacts from both sides. In

30 there is shown still another form of impedance matching, this being the type of transformer? described in an article by Sterba and Feldman in the" Proceedings of the .Institue' of Radio Engineers for July 1932, page 1163.

While Fig; 1 has been described as havingthree operating frequencies, it is to be understood that this is for illustrative purposes only, and that the number maybemade as large or as small as de sired. Thus, Fig. 2 shows the application of this same feature of invention to a system with the two operating frequencies f; and f2, The transmission line L from the terminal station, which may be either a transmitting or receiving station, goes to the junction-point C and there divides into the parallel branches a and b. the" one having the impedance matching device 2;, and 'the'other the matching device 2 From each of these, parallel wires come to the junction aint Cand'from there'extend to the antenna A. In the branch at," which we here assume is for the shorter wave length, and adjacent to the junction point C, is bridged the short transmission line Sl2 whichin this case is shown as open at both ndsand therefore'is of a length equal to a whole number of half wavelengths of the frequencywhich is to be passed. This selector S12 is connected at'a distance from the junction point equal to an odd number of quarter waves of f2, and the point 'of attachment to the selector is at a'distance from one of the open ends'equal to an odd nurnberbf quarter waves of f2. identically the same arrangement is followed in connection with the select or Siz, with reference to the juntion point C. A similar arrangement could be followed in the branch I), but a preferred alterna- ,tive, inasmuch asthe wavelength in this branch islonger, is to makethe selector $21 a short transmission line open at one end and short-circuited atthe other, and of a length equal to 'a'quarter waveofithe frequency fzwhich is to be passed. The distances of connection from the open end of the selector and from the junction point 'C are both an odd number of quarter waves of f1 which is to be excluded. ,The same arrangement holds for S 1.

v One ofthe features which I find to be important in connection with such wave antenna systems as here considered, istha-t there shall be no reflection from the remote end of the antenna to theterminal station. The elimination of such re- .flection may beobtained by connecting across the 2 remote end. of the antenna, which in all of'these figuresis taken to be of therhombiic type, a resistance ,T shown in Fig; 4. If this resistance T is chosen of the proper value to match the inipedance of theantenna'system'as seen looking from that resistance, then there will be no-reflection at that point. Since, however, the impedance of the antenna is a function of the frequency, it becomes necessary'to use a different terminating impedance for eachfrequency. This, obviously, may be accomplished by mechanical adjusting or switching of some form, but in my invention I provide a plurality of terminating" impedances each of which is physically connected to the circuit at all times, but is'electrically effective only for the frequency for which it is adapted. This is illustrated more fully in the single line diagram of Fig. 5 where, connected to the far end of the antenna A, are three terminating impedances T1, T2 andTs, each of avalue to give proper termination to the antenna for the corresponding frequencies f1, f2 and is. It is important, however, that the current of the frequency f1shall flow only in the termination T1, and similarly, for the other frequencies. To this end I introduce into the branch leading to T1. a plurality of selectors, one foreach of the frequencies to be excluded from that branch. Thus, in this illustration there are shown the selectors Smand S13, each at a distance from the junction point C equal to an odd number of quarter waves of the frequency to be excluded. The principle of the operation will be evident from the previous description, and

still more specifically by reference to Fig. 6 which shows the application to a system for two frequencies. In this case, in the branch a, which is to pass the shorter wave length, there is bridged the selector S12 open at both ends, and therefore a multiple of half wave lengths of the frequency to be passed. Similarly, in branch b, there is bridged a selector open at one end and closed at the other, and therefore an odd number of quarter'wave lengths of the frequency to be passed.

In some cases I find it desirable to have separate'terminal stations for the different operating frequencies, still using a single antenna A suitable for all the operating frequencies. As

shown in the single line diagram of Fig. '7 the stations 1, 2 and 3 have transmission lines com-' ing to the junction point C from which thecommon transmission line L extends to antenna A.

It'is important, in case the terminal stations are transmitters, that no power shall be fed fromone transmitter station to another, and I find that I can bring about this condition by introducing in each branchselectors ofthetype previously described, and properlypositioned with respect to the junction point C. This is shown in further detail in Fig; 8 which is a two line.

diagram for a two frequency system, the understanding ,of which will, be obvious from the description given heretofore. V

In some cases it, will bedesirable to combine the systems of Figs. 1 and 2 with that of Figs. '7 and 8, and such-combination is shown in Figs.

9.and 10, the first of these being a single line I diagram for'three terminalstations operating at different frequenciesin connection with a single antenna A. The transmission lineL in this Fig. 9 .willjin general, be quite long and the portions given over to the impedance matching devices and selectors would be as short as physically feasible. The details for the two frequency terminal 'stationsgand a single anten'na A, and a plurality of terminating impedances T1, T2 and ,harmonically related.

T3, this figure thus-representing the combination of'Figs'. 5 and 7. Similarly, Fig. 12 represents the combination of Figs. 6 and 8.

In some cases I find it desirable to use separate antennae A1, A2 and A3 for the different operating frequencies and at the same time" to have separate terminalstations, but having these all combined to operate over a single transmission line L. There thus comes into being two junction points C and C, and again, by the use of my selectors, there is present in any one branch only that frequency appropriate to that branch. This is shown in Fig. 13.

Finallyj-in' Fig. 14, I have shown the system of Fig. 10 but with a plurality of antennae A1 480,246, referred to above, but in that casethere is no limit to thenumb'er of branch circuits which maybe used. 1

While these selective devices may find their chief usefulness at a transmitting station where the energy of the system originates at a single source or a plurality of sources andis transferred toa single antenna or a plurality of antenna, they are equally applicable to a receiving station where the energy of the system originates at a single antenna ora plurality of 'antenna and is transferred to a single'receiver or a plurality of receivers.

Although in this. application I have shown my invention as applied to certain specific cases,

it is to be understood that various other applicationsand arrangements and combinations are possible, and these will be apparent to those skilled in the art. For example, operation may be singular on one antenna. or simultaneouson allantennae, the proper separation of the waves of different frequencies beingf effected at the junction points by the selective devices herein described. r

What is claimed is: I

1. In a. radio system an antenna adapted to operate on a plurality of frequencies and a terminal station, a transmission line connected therebetween, said line over a'portion of its length being divided into parallel paths one for each operating frequency, and means in each said path for matching the impedance between the antenna and the terminal station for the frequency corresponding to that branch.

2. In a radio system an antenna adapted to operate on a plurality of frequencies and a receiving station, a' transmission line connecting the antennato the receiving station, said line over a portion of its length being divided into parallel paths one for each operating frequency, and means in each said path for matching the impedancebetween the antenna and the receiv.

ing station for the frequency corresponding to that branch. I Y r 3. In a radiosystem an antenna'adapte'd to operate'on a plurality of frequencies and a transmitting station, a transmission line connected between theantenna and thetransmitting stationysaidline over a portionof its *lengthbeing nnual station, a transmission therebetween; said line. ove

.said branch for matching the im. the antenna and the tern ina divided into parallel paths one, for eachoperating frequency, and means in each said path for matching the impedance betweenthe antenna and the transmitting station, for the frequency corresponding to that branch, i

4. Ina radio system an antenna adapted to operate on a plurality of frequencies and a terminal station, a transmission line connected therebetween, said line over a portion of its length being divided into parallel paths one foreach operating frequency, means in'each said path for 7 matching the impedance betweenthe antenna and the terminal station for the frequency corresponding to that branch, and additional means in each branch to exclude all frequencies except the frequency corresponding to that'branch.

5. In a radiosystem an antenna adapted to operate on a plurality of frequencies and a terminal station, a transmission fline' connected therebetween, said line over a portionof its length being divided into parallel. paths one for each operating frequency, means in each. said path for hatching the impedance between the antenna andthe'terminalstation for thefree quency corresponding to thatbranch, and short transmission lines bridged across each branch and adjusted at the optimum length to. exclude from that branch all frequencies except the frequency corresponding to that branch.

:6. Ina radio system an antenna adapted to operateon a plurality of frequencies and ater minal station, a transmission line connected therebetween, said line over a portion of its length being divided into parallel paths one for each operating frequency, and transformers in each said path for matching the, impedance between theantenna and the terminal station for the frequency corresponding to thatbranch.

7. In'a radio system an'antenna adapted to operate on a plurality of frequencies and a terininal station,' a transmission line connected therebetween, saidline over a portionof its. length being divided intoparallel paths one for each operating frequency,transformers in each said path for matching the impedance between the antenna and the terminal station for the frequency corresponding to that branch, and short transmission lines bridged acrosseach branch and adjusted at the optimum length to exclude from that branch all frequencies except the frequency corresponding to. that branch.

8. The combination of claim 7 characterized by the location of said short transmissionlines,

one line on each side of each of the said transe formers for. the purpose set forth. j

9. The combination. of c frequency corresponding to that branch, and short transmission lines bridged across each branch of such length as to. exclude from that branch all frequencies except the frequency corresponding to that branch, some jof the bridges being open pairs of wires of half wave lengths of the frequency to be transmitted and someof nation for, the

pairs of wires short-circuited at one endand of quarter Wave lengths of the frequency to be transmitted. I a

11. The combination of claim 10 characterized by the fact that each short transmission line is connected to its branch at a distance from the junction of the branch and the main trans mission line-of aquarter of the Wave length of the frequency to be excluded. 7

12. The combination of claim- 10 characterized by the: fact that each short transmission line is connectedwtoits branch at a distance from the junction of the branch and the main transthe frequency to be excluded, and the connection to the short transmission lineis at a distance from an open, end thereof of a quarterof the Wave length of the frequency to be excluded.

Y 13. In a'radio system. an antenna adapted to operate on a plurality of frequencies and a terminal station's. transmission line connected therebetween, a plurality of inipedances termi- ,nating the antenna, one for each operating frequency, and each having its'impedance value determined by theyalue of the respective operating'fr'quen y, and means opcratively connected 1 the terminating.impedances to exclude em each such impedance all of the opf; crating 'requencies except the one corresponding to tnat'impedance;

lain a radio system an antenna adapted to .operateon a plurality of frequencies and a terniinalstation, a transmission line connected thcrebetween, a plurality of impedances in parallelterniinating the'antenna, each having its impedance value determined by the value of the respective operating frequency, short transmission lines bridged acrosseach impedance and adjusted in length andpositi'on to exclude from each such impedance all operating frequencies except the one corresponding to that impedance. i

15. The combination of claim lichara'cter- -ized by the fact that some of the bridges are pairs of yires short-circuited at one end and of a length equal-to an odd number of quarter Waves of the frequency to be transmitted and some are open pairs of Wines of a whole number of hal'fl'wave lengths of the frequency to be transmitted. 1 6.1he' combination of claim 14 characterized bylthe factthat 'sorneof the bridges are pairs of Wires shor't-circuited at one end and of a length equal to'ian odd number of quarter Waves of the frequency'to be transmitted, and that each short transmission. line is connected to its branch at a distance from the junction otthe branch and the main transmission line of a quarter of the wave len th of the frequency main transmission line of a quarter of the wave length of the frequency to be excluded and'the I connection to the short transmission line is at a distance from an open end thereof of a quarter of the wave lengtlrof the frequency to be excluded. j j

18. The combination of claim 14 characterized by the'fact that there is a bridging, circuit across each impedance for each frequency to be exeluded, and that some of the bridges are pairs of wires short-circuited at one end and of a length equal to an odd number of quarter waves of the frequency to be transmitted, and some are open pairs of wires of a whole number of half wave lengths of the frequency to be transmitted.-

19. In a radio system an antenna adapted. to operate on a plurality of frequencies, a plurality of terminal stations one for each operating frequency, transmission lines from each station to a common junction and a common transmission line therefrom to the antenna, and means in each of the first-named transmission lines to exclude all of the operating frequencies except the.

one appropriate to its terminal station, said means consisting of selective impedancesone for each frequency to be excluded and tuned to that frequency, each placed at a definite portion of a Wave length of the frequency for which it is tuned from the common junction point. I

20. In a radio system an antenna adapted to operate on a plurality of frequencies, a plurality of terminal stations, one for each operating frequency, transmission lines from each station to a common junction and a common transmission line therefrom to the antenna, and means in each of the first named transmission lines to exclude all of the operating frequencies except the one appropriate to its terminal station, said means consisting of short bridging transmission lines one for each frequency to be excluded and each placed at a definite portion of a wave length of the frequency which it is to exclude from the common junction point.

21. In a radio system an antenna adapted to operate on a plurality of frequencies, a plurality of transmitting stations, one for each operating frequency, transmission lines from each station to a common junction and a common transmission line therefrom to the antenna, and means in each of the first-named transmission lines to exclude all of the operating frequencies except the one appropriate to its transmitting station, said means consisting of short bridging transmission lines one for each frequency to be excluded and each placed at a definite portion of a Wave length of the frequency'which it is to exclude from the commonijunction point.

22. In a radio system an antenna adapted to operate on a plurality of frequencies, a plurality of receiver stations, one for each operating frequency, transmission lines from each station to a common junction and a commontransmission line therefrom to the antenna, and means in each of the first-named transmission lines to exclude all of the operating frequencies except the one appropriate to its receiver station, said means consisting of short bridging transmission lines one for each frequencyto be excluded and each placed at a definite portion of a Wave length'of the frequency which it is to exclude from the common junction point.

23. The combination of claim 5 characterized by a plurality of impedances in parallel terminating the antenna each with an impedance appropriate for one of the operating frequencies, short transmission lines bridged across each impedance and adjusted at the optimum length to exclude from each such impedance all the operating frequencies except the one corresponding to that impedance.

24. The combination of claim 19 characterized by the fact that the transmission line over a portion of its length is divided into parallel paths one for each operating frequency, means in each said path for matching the impedance between the antenna and the terminal station for the frequency corresponding to that branch, "and additional means in each branch to exclude all frequencies except the frequency corresponding to that branch, the combination being further characterized by a plurality of impedances terminat ing the antenna, one for each operating frequency and with an impedance appropriate for each operating frequency, and means associated with the terminating impedances to exclude from each such impedance all of the operating frequencies except the one corresponding to that impedance.

GEORGE W. GILMAN, 

